Oscillator



Dec. 27, 1949 M. T. REYNOLDS 2,492,767

OSCILLATOR Filed Nov. 12, 1947 +2 NET vom-AGE or: SCREENED GFuD'eInventor: Merl TR eyo lds,

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H i S Attcrey.

Patented Dec. 27, 1949 OSCILLATOR Y Meri T. Reynolds, Ballston Lake,N.Y., assigner to General Electric Co New York mpany, a corporation ofApplication November 12, 1947, Serial No. 785,261

9 Claims. (Cl. Z50-36) This invention relates to electronic circuits 5.1

obtaining negative transconductance and to electron discharge deviceoscillator circuits employing the phenomenon of negativetransconductance.

A general object of the invention is to provide improved electrondischarge device circuits obtaining negative transconductance.

, An object of the invention also is to provide an improved negativetransconductance oscillator.

v A more specic object is to provide an osci1- lator of the negativetransconductance type wherein the frequency determining tuned circuithas one terminal at ground potential. l

, -A further object is the provision of an oscillator comprising a smallnumber of components which will provide stable sine-wave signals withlow distortion over a wide range of frequencies.

An additional object is to provide an oscillator from which an outputvoltage of high intensity is obtainable without direct connection to thefrequency determining elements.

It is also an object of the invention to provide an oscillator whichwill become inoperative to generate oscillations upon disconnectionofthe inductance included in the tuned circuit.

Another object is to provide a `negative translconductance oscillator inwhich the tuned circuit inductance has no tapped connection.

rIt is a further specific object of my invention to provide an improvednegative transconduct-` ance oscillator operable over a wide band offrequencies, wherein one terminal of the parallel tuned circuit ismaintained at direct current ground'potential, wherein the otherterminal is connected to the third, or screened, gridrather than to therst grid, the first grid being directly grounded, and wherein operationup to very high radio frequencies is practicable without the necessityof providing tuned lter circuits to lsolate'the screen grid from the lowimpedancev power supply.

The novel features which I believe-to be characteristic of my inventionare set' forth with parcomponents and possessing additional advantages;and Fig. 3 is a group of curves explanatory of the operation ofoscillators according to the invention.

' Referring now toFig. 1, I have shown a pentaf grid discharge device Icomprising a grounded cathode 2, a rst grid 3, which is also grounded, ascreen grid consisting of grid elements 4 and 5 disposed on oppositesides of a second control grid being the third grid from the cathode,which maybe referred to as the screened grid. Grounded suppressor grid1, the fifth grid from the cathode, is arranged inside anode 8, theanode being directlyconnected to a source of positive B+ potential, suchas the battery 9, the negative terminal of the source being grounded.The

impedance of the potential source is made low for the frequencies atwhich operation is desired by connecting a capacitor I0 of high capacityfrom B+ to ground.

A frequency determining parallel-tuned circuit comprising inductance IIand condenser I2 is connected between control grid 6 and ground, and afeedback circuit including a series condenser I3 is arranged to feedback oscillatory energy from the screen grid 4 and 5 to the tunedcircuit. vAs explained below the feedback through condenser I3 is inphase with the voltage appearing on control gridV 6. If the value ofcondenser I3 is made low, the oscillator output will very closelyapproach a true sine wave. Higher values, however, may be `desirable toinsure strong oscillation Aover a wider range of supply voltagevariations or over a wider range of frequencies. B+ supply for thescreen grid is through a load resistor I4, across which the outputsignal is developed. f

A modification of the device is shown in Fig.2'

the secondfgrid 4 and fourth grid 5, comprising the screen grid, areconnected to the B+ potential source, battery 9, through a load resistorI4, and 'the tuned circuit comprising inductance II and parallelcapacitor I2 has; one terminal grounded and the yother connected throughcapacitor I3 to feed back energy4 to the screenedgrid' s.

The anode tains a lload resistor I8 across; which the oscil- 65 latingoutput voltage is developed. The resistor circuit inthe devicecf Fig. '2

may conveniently be arranged as a potentiometer, as shown, in order thatthe output voltage derived from the movable contact may be adjusted inintensity. A direct current blocking capacitor I1 may be connected inseries with the output terminal in a known manner, if desired.

The operation of the oscillators of Fig. 1 and Fig. 2 may be bestexplained with reference to Fig. 3. As shown by the curves of Fig. 3,which are labeled to indicate current (I) or voltage (E) for theelements of tube I, an increase in the potential of the third grid 6,along the abscissa of the chart, produces a decrease in the current,curve 14,5, to the interconnected second and fourth grids 4 and 5, and aresultant increase in the potential thereon, curve E45, because of thelower current through resistor I 4, if the discharge device I is biasedto operate at approximately the operating point indicated on the chartby a vertical dashed line. The increase in potential of grids 4 and 5occurs simultaneously with the increase in potential of the third orscreened grid 6 and provides an energy feedback to grid 6 throughcapacitor I3. The energy thus fed back is suicient to overcome thecircuit losses, and oscillations thus occur which are at the resonantfrequency of the tank circuit I I, I2. It will be understood that theresonant frequency will be affected by the inherent capacitance of thecircuit elements, which is effectively in parallel with capacitor I2, aswell as to a small extent by the inherent inductance of the circuit.

The anode 8 of the discharge device in Fig. 2 is provided with a loadresistor IB connected in series to the source 9 of positive operatingpotential. The resistor may conveniently comprise a potentiometerresistance provided with a variable tap as shown to select a desiredvalue of output voltage for furnishing to external apparatus throughcapacitor I'I. The device of Fig. 2 exhibits an anode voltage curve suchas Ea in Fig. 3, whereas, of course, the anode voltage of the device ofFig. 1 is constant and would appear on the chart as a horizontalstraight line.

An oscillator according to either of Figs. 1 or 2 of the drawings haswide frequency range and stability characteristics which particularlyadapt them to use in devices for determining the inductance orcapacitance of elements which may be inserted' in the tuned circuit II,I2.

For instance. if the value of the inductance of element II is unknown,but the capacitance of condenser I2 is available from a calibrated dialor otherwise, the condenser I2 may be adjusted until the frequency ofthe oscillator coincides with that of an external standard oscillator.The resonant frequency of the tuned circuit Il, I2 and the value of thecapacitance I2 being both known, the inductance of element I I isreadily calculated.

For such use of the oscillator, it will be obviously desirable that tapson the inductance in the tuned circuit should be unnecessary, that'oneend of the inductance should be grounded for both direct currents andalternating currents, that the oscillator should be inoperative if thereis no inductance element in the circuit, that there should be nosubstantial change under varying output load conditions, that theoscillator should be stable, relatively unaffected by supply voltagevariations, and that it should provide oscillations over a very widebandol frequencies.

Thev oscillator according to thisinvention successfully meets all ofthese criteria, is simple in construction, is composed of ordinarycommer- 4 cially available components, and the values of the componentsare not critical, except, of course, that for accurate results, it maybe necessary to provide accurate calibration of the values of inductanceII or capacitor l2 if the value of one of these two elements is knownand is to be determined as outlined above.

While I have shown only certain preferred embodiments of my invention byway of illustration, many modifications will occur to those skilled inthe art and I therefore wish to have it understood that I intend, in theappended claims, to cover all such modifications as fall within the truespirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electron discharge device oscillator system obtaining negativeytransconductance, comprising a vacuum tube having therein a cathode, ai-lrst grid, a screened grid, a screen grid and an anode, a screengrid-to-cathode circuit comprising a source of direct current operatingpotential, a load resistor extending from said screen grid to a firstpoint in said circuit which is positive with respect to said cathode, aparallel tuned tank circuit connected between said screened grid and asecond point in said circuit which is negative with respect to saidiirst point, a feedback coupling from said screen grid to said screenedgrid, a connection for said rst grid to said circuit for maintainingsaid'first grid at a potential negative with respect to said firstpoint, and means for energizing said anod Y 2. An oscillator comprisinga tuned circuit with two terminals, an electron discharge device with ananode, a cathode, a control grid and an anode grid, said anode gridcomprising two sec tions respectively disposed on opposite sides of saidcontrol grid, said grids being disposed between said anode and saidcathode, means for establishing a potential gradient between said anodeand said cathode such that an increase Vin control grid potential causesan increase in anode grid potential, and means to feed back to saidcontrol grid without substantial phase shift changes in said anode gridpotential, said tuned circuit being connected in a control-grid-'toAcathode circuit.

3. In an oscillator with two output terminals and including a resonantcircuit, an electron discharge device with an anode, a cathode and vegrids between said cathode and anode, the first and fifth of said gridsfrom said cathode being connected to a point at ground potential, one ofsaid terminals being connected to said ground point, the other of saidterminals being connected' to the second and fourth of. said grids, saidin-` terconnected second and fourth grids being conan nected through aload impedance to a source of positive potential, regenerative feedbackcoupling from said second and fourth grids to the' third of said grids,means for providing operating potentials to saidcathode and said anode,

: and means for biasing said third grid to a po tential relativelynegative with respect to said interconnected second and fourth grids.

4. An oscillator comprising a tuned circuit, an

electron discharge device with an anode, a cath` v g ,ode, a controlgrid and an anode grid, saidanode grid comprising two sectionsrespectively 'dis-A posedfon opposite sides of said control grid, saidgrids being disposed Vbetween said anode and said cathode, means forestablishing a potential gradient between said anodel and said cathodesuch!y that an increase in control grid potential causes 5 an increasein anode grid potential, means to feed back to said control grid withoutsubstantial phase shift changes in said anode grid potential, said tunedcircuit being connected in a control-grid-to-cathode circuit, and outputmeans associated with said anode.

5. In a negative transconductance oscillator including a resonantcircuit, an electron discharge device with an anode, a cathode and atleast four grids between said cathode and anode, means for supplying arelatively large positive operating potential to said anode with respectto the potential of said cathode, means maintaining not more thanrelatively small respective biasing potentials from the second and'fourth grids to said cathode, said last means comprising said resonantcircuit in series with said second grid. means interconnecting andmaintaining the first and third grids at a more positive potential thanany of the other grids in said device and less positive than said anode,an inphase feedback circuit from said interconnected rst and third gridsto said second grid to sustain oscillation in said resonant circuit.

6. An electronic oscillator comprising an electron discharge device withan anode, a cathode, a control electrode, a screen electrode in twoconnected portions arranged respectively on opposite sides of saidcontrol electrode to screen said control electrode toward said anode andtoward said cathode, and a grid adjacent said anode, said anode beingconnected to a point in a source of potential positive with respect tosaid cathode, means comprising a series impedance connecting said screenelectrode to a point of said source of potential not more positive thanthe point of connection for said anode, said grid being maintained at apotential negative with respect to the potential of said screenelectrode to form with said anode a virtual cathode for said screenelectrode, means comprising another impedance for biasing said controlelectrode negative with respect to said screen electrode, means forminga resonant circuit with one of said impedances, and means for feedingback in-phase energy from said screen electrode to said controlelectrode.

'1. An electronic circuit obtaining negative transconductance comprisingan electron discharge device with an anode, a cathode and five grids,said grids being arranged in sequence from said cathode to said anode,means maintaining the first and fifth of said grids substantially at axed reference potential, means providing a positive operating potentialto said anode, means maintaining said cathode at a potential lesspositive than the cut-oir potential established by the potential of said'rst grid, means for providing a positive operating potential to thesecond and fourth of said grids together through a load impedance, meansfor biasing the third of said grids to a potential substantially thesame as that of said rst grid and for applying a signal to said thirdgrid whereby said signal produces a corresponding 'in-phase signalacross said load impedance.

8. A circuit obtaining negative transconductance comprising an electrondischarge device with an anode, a cathode, and five grids in sequencebetween said cathode and said anode, means providing positive operatingpotentials to said anode and through an impedance to the second andfourth of said grids, said second and fourth grids being interconnected,means for biasing the first grid with respect to said cathode to apotential within the operating range of said device, means for biasingthe third and fifth grids to substantially the potential of said firstgrid, and means to provide a signal to said third grid whereby acorresponding signal in phase with the signal on said third grid appearson said second and fourth grids.

9. A negative resistance comprising an electron discharge device with ananode, a cathode and at least four grids, means providing a positiveoperating potential to said anode with respect to said cathode, two ofsaid grids comprising a screen grid, another of said grids comprising acontrol grid and being disposed between said last mentioned two gridsthereby to be screened from said anode and from said cathode, the fourthof said grids being disposed between said screen grid and said anode,means comprising an impedance in series with said screen grid providingan operating potential to said screen grid not more positive than saidanode potential, means for biasing said fourth grid negative withrespect to said screen grid, means for biasing said control gridnegative with respect to said screen grid, and a capacitor connected tofeed back in-phase energy from said screen grid to said control grid.

MERL T. REYNOLDS.

REFERENCES CITED The following references are of record in the ille ofthis patent:

UNITED STATES PATENTS Number Name Date 1,943,302 Dow Jan. 16, 19342,119,357 Schalkwijk May 31, 1938 2,230,097 Whitaker Jan. 28, 1941

